You've got your bottles all nicely sterilised and ready for baby's feed. Warm and cosy, he guzzles down his milk like a hungry little lamb. But is what he is drinking safe?

To add to the range of anxieties which torment parents, some scientists fear that a chemical in babies' feeding bottles may be harmful.

After being sterilised in a microwave or when the bottle becomes slightly scratched or cloudy with age, this chemical, bisphenol A, leaches out into the milk and is ingested by your baby, they believe.

Nearly all bottles on the British market are made of polycarbonate, which contains the chemical. In Japan and South Korea, however, most parents now refuse to use such bottles after health fears there three years ago. Not all experts agree that bisphenol A is harmful.

Three years ago, Department of Trade and Industry-backed research found it was released from used babies' bottles which had been subjected to bottle brushing and/or dishwashing and sterilisation. It was not detected in the liquid in new polycarbonate bottles.

At the Foods Standards Agency , where research is being conducted into bisphenol A in the lining of food cans, there is little concern about babies' bottles.

A spokesman said: "The polymer used in polycarbonate bottles is very robust. The bisphenol A is bound tightly into the polymer and this leads to it remaining there rather than migrating into food. This is not the same situation as in can coatings." But parents can now decide themselves. Either they can replace bottles regularly or investigate the product of a Newcastle company, One Step Ahead, which has brought out a bottle made of "B-free" plastic.

Bisphenol A is a hormone disrupting agent. These are the range of chemicals often referred to as "gender benders" which have caused disturbing fertility problems in wildlife from freshwater British fish to the Arctic polar bear.

Matthew Wilkinson, UK toxics policy officer with the World Wide Fund for Nature, says more scientists are now linking them to reduced sperm counts, poor sperm quality and higher incidence of diseases such as testicular and prostate cancer in humans.

"Babies are extremely susceptible to the impacts of hormone disruption," says Mr Wilkinson.

"The ratio of chemicals to body weight often means they are receiving much larger doses than adults."

The B-free plastic is tricky to mould and so more costly. But the technology is there and the Dr Brown model is an attempt to corner a potentially very lucrative market.

One Step Ahead director Piero Alberici says: "As many parents know, baby bottles don't stay shiny and clear for long and it is when they become scratched and discoloured that the problems can start." Mr Wilkinson said: "Piero's work is giving British parents a choice and that's what's important."

Dr Brown's Natural Flow bottles are available on mail order or its website.